Inkjet printing has increased in popularity in recent years due to its relatively high speed and excellent image resolution. Moreover, an inkjet printing apparatus used in conjunction with a computer provides great flexibility in design and layout of the final image. The increased popularity of inkjet printing and the efficiencies in use have made inkjet printing an affordable alternative to previously known methods of printing.
In general, there are three types of inkjet printers in widespread use: the flat bed printer, the roll-to-roll printer and the drum printer. In the flat bed or large-format printer, the medium or substrate to receive the printed image rests on a horizontally extending flat table or bed. An inkjet print head is mounted on a movable carriage or other type of mechanism that enables the print head to be moved along two mutually perpendicular paths across the bed. The print head is connected to a computer that is programmed to energize certain nozzles of the print head as the print head traverses across the substrate, optionally using inks of different colors. The ink on the substrate is then cured as needed to provide the desired final image.
Large-format inkjet printers generally move a scanning carriage containing one or more print-heads in a transverse or horizontal direction across a print medium, while incrementally advancing—or “stepping”—a print medium in a lengthwise or vertical direction in-between successive printing passes, or scans, of a reciprocating carriage. Inkjet printing involves placing large quantities of tiny ink droplets formed by one or more ink-emitting (or “jetting”) nozzles onto predetermined locations on a print medium or substrate. The ink droplets solidify or dry on the print medium forming small dots of color. A quantity of these small colored dots when viewed at a nominal distance will be perceived as a continuous-tone visual image. To increase the rate of print production, a print-head typically employs numerous jetting nozzles per color of ink ganged together in a suitable arrangement to create a band or “swath” of printed area that is much wider than otherwise would be obtainable from a single jetting nozzle. Usually, several linear arrays of jetting nozzles are disposed in a print-head in an orientation parallel to the direction of media travel (X-axis) and perpendicular to the direction of carriage travel (Y-axis). Both text and graphic images may be printed with inkjet printing.
Large scale digital color ink jet printers are described, for example in U.S. Pat. No. 6,789,876 to Barclay et al., the subject matter of which is herein incorporated by reference in its entirety.
In large format inkjet printers, the printhead is typically operable to simultaneously print ink of different colors. Preferably, the print head has at least four sets of nozzles that are in communication with at least four corresponding ink sources. As a result, the printhead is operable to simultaneously print at least four inks of different colors so that a wide color spectrum in the final printed image can be achieved.
Inks that are commonly used in inkjet printers include water-based inks, solvent-based inks and radiation-curable inks. Water-based inks are used with porous substrate or with substrates that have a special receptor coating that is capable of absorbing water. Typically, water-based inks do not perform well when used for printing on non-coated, non-porous films.
Solvent-based inks used in inkjet printers are suitable for printing on non-porous films and are able to overcome the problems associated with water-based ink formulations. However, these solvent-based inks contain a large volume (typically at least 90%) of organic solvent by weight. As the solvent-based ink dries, the solvent evaporates and may present an environmental hazard. In addition, inkjet printers using either solvent-based or water-based inks must remove relatively large quantities of solvent or water before the printing process is complete and the ink is dry such that the resulting printed product can be handled.
As a result of the problems with water-based and solvent-based inks, radiation-curable inks are herein proposed to be used for printing on a variety of non-coated, non-porous substrates. The use of radiation curing enables the ink to dry quickly without the need to drive off large quantities of water or solvent. As a result, radiation-curable inks can be used in the high speed ink jet printers proposed herein.
While large scale inkjet printers are well known, various improvements in these printers are necessary in order to provide more efficient and higher quality printing on a variety of print media, including for example, paper, fabric, corrugated media, plywood etc.